The field of this invention is that of torque sensors and the invention relates more particularly to a compact and reliable torque sensing device particularly adapted for use in an automotive power steering system.
Conventional automotive power steering systems utilize a torque sensing device to detect torque applied to a vehicle steering shaft. They provide a control signal corresponding to the torque for regulating operation of a motor to provide a desired degree of assisting torque to the steering shaft. Similar torque sensors are proposed or used in a variety of other torque measurement and control applications, such sensors including strain gage torque detecting systems, magnetic leakage flux systems, hydraulic systems and the like. In most automotive steering systems presently in use, the torque sensor device includes a torque transmitting member or bar which twists relatively easily under an initially applied torque to provide a control motion and includes lost motion means which engage after a predetermined degree of twist has occurred for reliably transmitting any additional applied torque while also protecting the torque bar from damage. In the typically used automotive steering systems, the degree of twist provided in the torque bar regulates a hydraulic system to provide the desired degree of assisting torque to the steering shaft. However with increased use of computer control of automotive engine systems, there has been increased interest in electrical torque sensing devices using electromagnetic torque detecting means and the like to be more compatible with the computer engine controls. Many of such electrical systems have now been proposed. A torque sensing device using a magnetic leakage flux has been considered desirable in many respects but is also found to be relatively expensive to manufacture and to be relatively sensitive to variations in axial alignment of device components and to other factors which are difficult for a manufacturer to control. It would be desirable if a more reliable and inexpensive electrical torque sensing device could be provided particularly for use in automotive power steering systems.